Firefox 21.0 Date added: May, 14th 2013 - (Open Source)

What's new in this version:

New:
- Enhanced three-state UI for Do Not Track (DNT).
- Firefox will suggest how to improve your application startup time if needed.
- Preliminary implementation of Firefox Health Report (see FAQ).

Changed:
- Ability to Restore removed thumbnails on New tab Page.
- Add-ons History API removals in Places.
- CSS -moz-user-select:none selection changed to improve compatibility with -webkit-user-select:none (bugs 816298).
- Graphics related performance improvements (bugs 809821).
- Removed E4X support from SpiderMonkey.

Developer:
- Implemented Remote Profiling.
- Integrated, Add-on SDK loader and API libraries into Firefox.

HTML5:
- Added support for <main> element.
- Implemented scoped stylesheets.

FixedL
- Some function keys may not work when pressed (833719).
- Browsing and Download history clearing needs unification to avoid confusion on clearing download history (847627).